This invention relates to method and apparatus for drying wafers.
It has particular application to methods and apparatus which spin dry a wafer by gripping the wafer on its edge to eliminate contact with the face of a wafer and possible stains which can result from such face contact.
The present invention also has specific application to a carriage mechanism which brings a wet wafer into the drying station at one level and which takes the dry wafer out of the drying station at a different level to prevent any contact between the dry wafer and residual moisture at the incoming level.
Wafers that are used for the manufacture of integrated circuits must be thoroughly cleaned in order to reduce defects in the finished integrated circuits. Because the circuits themselves are very small, any foreign material, such as dirt, water stains, etc., can cause an unacceptably high rejection rate in the final product.
The wafers must therefore be cleaned on both sides, and this presents a problem of how to dry a wafer in a way to maintain cleanliness while eliminating possible stains.
It is generally considered that centrifugal drying is better than blow drying of a wet wafer. Centrifugal drying helps to overcome the surface tension and resultant clinging of moisture around the edge of a wafer that can result from blow drying.
Spin drying has been accomplished in the prior art by a vacuum chuck which gripped the wafer on the lower face of the wafer. This type of chuck mechanism has presented the problem of stains resulting from the contact between the chuck and the bottom face of the wafer.
One of the primary objects of the present invention is to spin dry a wafer using a wafer holder which grips the wafer on the edge of the wafer, rather than on a face, to eliminate contact and resultant stains on the wafer face.
Getting the wafer dry is one problem; keeping the wafer dry is another problem.
The wet wafer must be brought into a drying station, dried and then removed from the drying station. There can be a problem in keeping the wafer dry as it is handled at the drying station after the spin drying operation if there is residual moisture at the drying station resulting from the conveyor mechanism that brought the wet wafer into the drying station.
It is another primary object of the present invention to handle the wafer in a way so that the dry wafer conveyor mechanism is isolated from the wet conveyor mechanism to prevent any contact between the dry wafer and residual moisture on the wet wafer conveyor mechanism.